Some Problems of Reproduction: a Comparative Study of ...

4 MABCUS M. HARTOG.
of gametes by rapidly repeated divisions of a cell—the
gametogonium;
(2) That the alleged nuclear excretions in the Metazoan egg
and the Ciliate " gamete/' &c, represent true gametes arrested
in their development;
(3) That the so-called "excretions" of protoplasm in plants
are of various kiuds, many of which are homologous neither
with the former process nor with one another;
(4) That the use of the rapid preliminary divisions is a
purely physiological one; that is, to induce by exhaustion
the same reproductive incapacity that would otherwise
require a long series of slowly repeated divisions.
On these lines we can account for all the facts, from the
simplest cases of the formation of isogametes to the most
peculiar phenomena of oogeny and spermatogeny; phenomena
which the sexual replacement theories of Minot, Balfour, and
van Beneden, on the one hand, and the more complex replacement
theory of Weismann, on the other, only profess to
explain in the higher groups. The views here put forward
are essentially a development and extension of what we may
term the "morphological theory" of polar bodies, first enunciated
by Giard, Biitschli, Whitman, and Mark, 1 and advocated
especially by the Hertwigs. It will not seem strange that
this view has never had full justice done it when we reflect
that it is to men who have worked especially at the Metazoa
that we owe the greatest debt for shaping our biological
theories; and that our gratitude has, perhaps, led us to be
too unquestioning in our attitude of discipleship to such respected
masters as Balfour, van Beneden, and Weismann. 2
The exposition of the processes of gametogeny naturally leads
1
Mark was the first definitely to express the view that the polar bodies
represent abortive ova ; see " Maturation, Fecundation, and Segmentation of
Limax campestris," in 'Bull. Mus. Comp. Zool. Harv. Coll./ vol. vi, 1881.
2
I may say that 1 never doubted that some replacement theory of
fertilisation was sufficient to cover the facts, till I read and meditated over
Maupas's account of the conjugation of the Ciliata ; and this it was that first
weakened'my belief, not only in replacement theories, but also in the " preliminary
excretion " theory on which the others were founded.